This invention relates to electrostatic precipitators used in removing dust particles suspended in air or other gases.
Many types of precipitators have been developed including those that involve single stage ionization and collection, i.e., the Cottrell type, where the dust particles are collected in the same electric field in which they are ionized or charged. Although the invention has special applicability to the single-stage precipitators, it can be used effectively with other types, such as those that charge the particles in one field and collect them in another.
In the Cottrell type precipitator, the dust-laden gas is introduced into a main flow chamber at a relatively high velocity and passed through one or more banks of emitting and collecting electrodes which extend substantially vertically through the chamber. Each emitting electrode is a wire charged to a relatively high DC voltage. An electric field is thereby set up between the emitting and collecting electrodes so that the dust particles are charged with the same polarity as the emitting electrodes, causing the particles to be collected on the collecting electrodes, which are platelike in shape. The collecting electrodes are vibrated or rapped periodically, and the collected dust particles fall by gravity through openings at the bottom of the chamber leading to collecting hoppers or bins.
Because of the mounting public demand for cleaner air, modern air pollution control equipment must be able to operate at high efficiency rates. Specifications calling for the removal upwards of 99 percent of the dirt contained in air discharged into the atmosphere are not uncommon. It has been found that electrostatic precipitators are capable of operating at these high levels.
One popular usage of electrostatic precipitators is in large industrial plants where the collecting electrodes are normally 30 feet in length and longer. To maintain their high efficiency, the particles attracted to the collecting electrodes must first be efficiently conveyed into the hoppers at the bottom of the flow chamber. In addition, little or none of the dust particles in the hoppers should be re-entrained in the rapidly flowing stram of gas. Many designs have been suggested and tried, with varying degrees of success. In order to provide the high efficiency desired in these precipitators such designs have included the use of baffles or specially designed electrodes to control gas flow, lower gas velocity, higher electric charges, variations in the techniques of rapping or vibrating the collecting electrodes, and different types of electrical energization. However, such modifications involved primarily directing the gas flow through the precipitator chamber or facilitating the gravitational transfer of dust particles from the collecting electrodes downwardly toward the bottom of the chamber.
One problem, to which this invention is directed and which has not been overcome in the past, is preventing re-entrainment of dust that has been collected in the hopper or carried by gas near its entrance.